The Role of Spermidine/spermine N1-acetyltransferase in Endotoxin-induced Acute Kidney Injury

The expression of catabolic enzymes spermidine/spermine N(1)-acetyltransferase (SSAT) and spermine oxidase (SMO) increases after ischemic reperfusion injury. We hypothesized that polyamine catabolism is upregulated and that this increase in catabolic response contributes to tissue damage in endotoxin-induced acute kidney injury (AKI). SSAT mRNA expression peaked at threefold 24 h following LPS injection and returned to background levels by 48 h. The activity of SSAT correlated with its mRNA levels. The expression of SMO also increased in the kidney after LPS administration. Serum creatinine levels increased significantly at approximately 15 h, peaking by 24 h, and returned to background levels by 72 h. To test the role of SSAT in endotoxin-induced AKI, we injected wild-type (SSAT-wt) and SSAT-deficient (SSAT-ko) mice with LPS. Compared with SSAT-wt mice, the SSAT-ko mice subjected to endotoxic-AKI had less severe kidney damage as indicated by better preservation of kidney function. The role of polyamine oxidation in the mediation of kidney injury was examined by comparing the severity of renal damage in SSAT-wt mice treated with MDL72527, an inhibitor of both polyamine oxidase and SMO. Animals treated with MDL72527 showed significant protection against endotoxin-induced AKI. We conclude that increased polyamine catabolism through generation of by-products of polyamine oxidation contributes to kidney damage and that modulation of polyamine catabolism may be a viable approach for the treatment of endotoxin-induced AKI.